Tin plate identification



United States Patent "ice 3,281,221 TIN PLATE IDENTIFICATION Andy A.Denuzzio, Aliquippa, Pa., assignor to Jones &

Laughlin Steel Corporation, Pittsburgh, Pa., a corporation ofPennsylvania No Drawing. Filed Feb. 28, 1964, Ser. No. 348,272 8 Claims.(Cl. 29--191) This invention relates to tin plate which is positivelyidentified as to source. It is more particularly concerned with tinplate which is marked or branded in such a way that the marking isnormally invisible, but can be discovered by stripping off the tin plateor the tin coating together with the tin-iron alloy layer.

Tin plate is commercially produced by steel manufacturers and is soldprincipally to manufacturers of tin cans. The tin cans in turn are soldto packers of foods of various kinds. The tin plate is shipped to thecan manufacturer in the form of sheets or of coils and is cut up by himinto can body blanks and can end blanks which he then fabricates intotin cans. The tin surface of both the body blanks and the end blanksmust be free of all foreign substances as otherwise the food packed inthe cans could be contaminated. Although the tip plate re ceived by thecan maker is identified as to source, this identification does not carryover to the body blanks and end blanks stamped therefrom. Consequently,although the cans shipped to a packer are identified as to the canfabricator, they are not identified as to the maker of the tin plate.Therefore, prior to my invention to be described, if canned food spoiledbecause of defective tin plate, there was no certainty of identifyingthe tin plate as being the product of one supplier if the can maker usedtin plate from several sources, as is generally the case.

It is an object of my invention, therefore, to produce tin plate whichcarries a mark indicative of its source even when it is cut up andfabricated into cans. It is another object to provide such tin platehaving an identifying mark which is visible only when the tin coating orthe tin coating and the tin-iron alloy layer are removed. Other objectswill appear in the course of the description of my invention whichfollows.

The tin plate of my invention comprises the conventional thin still basehaving the conventional tin coating which may be appliedelectrolytically or by hot dipping. Electrolytic tin plate isconventionally flow brightened, that is, heated briefly to a temperatureslightly above the melting point of tin to flow the matte tin deposit,and then quenched. Both types of conventional tin plate are, therefore,heated above the melting point of tin during their manufacture, and thisheating brings about an alloying of the tin and iron at the tin-ironinterface which is visible under the microscope as a thin layer of thisalloy intermediate the tin and iron. The surface of the steel base ofthe preferred tin plate of my invention is chemically treated prior totinning so as to etch the steel base to a slight degree. This etching,which is clearly visible against the steel base, does not deleteriouslyaffect the adherence of the tin thereto or the formation of tin-ironalloy between base and tin coating when the tin plate is heated.However, the appearance of the tin-iron alloy in the etched areas isdifferent from that in the unetched areas of the base. As the tin-ironalloy is covered by the tin coating, the tin plate, as it leaves the tinpot or the flow brightener of an electro-tinning line, displays noevidence of the etching that has taken place. However, if the tin isstripped from the tin plate, the tin-iron alloy, which then becomesvisible, displays a marking corresponding to the etched area of the basebeneath it. If the tin-iron alloy is also stripped, the steel basedisplays the 3,281,221 Patented Oct. 25, .1966

mark produced by the etching. I prefer to apply the chemical to thesteel base of my tin plate in an over-all pattern such that a pluralityof repeats will appear on each can body blank and each can end blankwhich may be stamped therefrom. Thus, if a can made from tin plate of myinvention proves defective, the supplier of the tin plate can beidentified by cutting a sample from the can and stripping the tin or thetin and the tin-iron alloy therefrom.

As the great bulk of the tin plate now being sold is tinnedelectrolytically, I shall first describe the manufacture of my tin platein that context. I apply my chemical etchant to the surface of the steelstrip after the strip has been cleaned but prior to its entrance intothe electrotinning bath. Preferably, the chemical is applied by a rubberroller, the surface of which is cut out or embossed into the desiredpattern. Etching begins immediately, but stops when the etchant iswashed off by the bath solution into which the strip passes. In theelectro-plating bath, tin is plated onto the strip in the conventionalmanner, the etching being insufficient to result in any change ofexternal appearance of the deposited tin. I prefer to use the so-calledhalogen electrolyte of US. Patent 2,407,579 granted to E. W. Schweikheron September 10, 1946. When the strip is flow brightened, the heatingaifects the tin-iron alloy layer formed thereby so that its appearanceover those etched areas is different from its appearance over unetchedareas. The external surface of the brightened tin plate shows no markingat all.

In the manufacture of hot dipped tin plate, I apply my chemical etchantto the steel just before it enters the tin bath. Etching beginsimmediately, but I find that the steel is in the bath such a short timethat the etching does not interfere with the adherence of the tin to thesteel. As in the case of the electro-tinned steel, the etching alsoaffects the appearance of the tin-iron alloy layer above the etchedarea, but does not mark the tin coating.

My preferred etchant is an 8% to 12% aqueous solution of ferricchloride. Those skilled in the art will have knowledge of other etchantsthat will produce the same effect.

My preferred new tin plate produced as I have here described, comprisestherefor a steel base having an etched marking thereon which contrastswith its backgroundthe base, a tin-iron alloy layer in immediate contactwith the steel base, that layer also having a marking thereon whichcontrasts with its backgroundthe tiniron alloy layer, and a reflowed tincoating which exhibits no marking. The marking on the tin-iron alloy isimmediately above the corresponding marking on the base. When the tincoating is stripped from my tin plate, which may be accomplished byknown methods, the marking on the tin-iron alloy layer contrasts withits background and is clearly visible. When the tin-iron alloy layer isalso stripped from my tin plate, which may also be accomplished by knownmethods, the marking on the steel base contrasts with its background andis clearly visible.

I claim:

1. A new article of manufacture comprising tin plate having on the steelbase an etched mark which contrasts with its background so as to beclearly visible thereagainst when the tin coating is stripped therefrom.

2. The article of claim 1 in which the etched mark is a chemicallyetched mark.

3. The article of claim 1 in which the mark is invisible beneath the tincoating.

4. The article of claim 2 in which the chemically etched mark is thereaction product of the steel base and ferric chloride.

5. A new article of manufacture comprising tin plate having a tin-ironalloy layer intermediate the steel base and tin coating and having onthe steel base an etched mark which contrasts with its background so asto be clearly visible thereagainst When the tin coating and tinironalloy layer are stripped therefrom.

6. The article of claim 5 in which the tin plate is electrotinned andflow-brightened tin plate.

7. The article of claim 6 in Which the electrotinned tin plate ishalogen electrolyte tin plate.

8. A new article of manufacture comprising tin plate having a tin-ironalloy layer intermediate the steel base and tin coating and having onthe steel base an etched mark and on the tin-iron alloy layer acorresponding mark immediately above the etched mark and occasionedthereby, which corresponding mark contrasts With its background so as tobe clearly visible thereagainst When the tin coating is stripped fromthe tin plate.

References Cited by the Examiner UNITED STATES PATENTS 10 DAVID L. RECK,Primary Examiner.

HYLAND BIZOT, Examiner.

R. O. DEAN, Assistant Examiner.

1. A NEW ARTICLE OF MANUFACTURE COMPRISING TIN PLATE HAVING ON THE STEELBASE AN ETCHED MARK WHICH CONTRASTS WITH ITS BACKGROUND SO AS TO TO BECLEARLY VISIBLE THEREAGAINST WHEN THE TIN COATING IS STRIPPED THEREFROM.